The scientific underpinning of the applied test methods included a thorough consideration and mitigation of testing limitations, for example:
- Testing of a device per ISO 18562 only captures a “snapshot” of device performance during degradation, and it may not be known whether there will be maxima in concentration of hazards (i.e., VOCs or particulates). To address this, testing was performed on multiple Used devices with differing amounts of patient usage and observed visual foam degradation, and on Lab-Aged foam that had been intentionally degraded to different degrees. Therefore, multiple “snapshots” of potential patient exposure can be captured as a function of device degradation to determine if a patient health risk may exist during the degradation process.
- Lab-Aging of foam is being used to induce various levels of foam degradation in controlled conditions without contamination from the environment, for comparison to levels of degradation in Used devices. Lab-Aging conditions are not intended to be predictive of foam degradation progression observed in Used devices. Differences may exist in how the Lab-Aged PE-PUR foam degrades compared to the Used foam over the lifetime use of the device, and these differences were considered in the completed risk assessments.
- ISO 18562-2 testing of devices quantifies the concentration of respirable particulates based only on their size range (i.e., up to 10 µm in diameter), but does not measure non-respirable particles (i.e., greater than 10 µm), nor does the standard characterize the chemicals present in particles detected. To address this, additional testing in accordance with ISO 10993 and very conservative assumptions were included such as a risk assessment calculation assuming that all of the foam in the device could become degraded and contact the patient, and chemical characterization and toxicological risk characterization of chemicals present in PE-PUR foam in accordance with ISO 10993-18 and -17 .
- Visual inspections are qualitative in nature and do not quantify VOCs or particulates within or emitted from a device. The visual inspection results did not contribute to the risk assessment calculation. While visual inspections have identified visual foam degradation in a limited number of first-generation DreamStation devices (0.5% of Used devices from the US and Canada, self-reported without ozone use), the associated risk assessment very conservatively assumed that all first-generation DreamStation, System One and DreamStation Go users could be exposed to all of the PE-PUR foam within the device, and that all of that PE-PUR foam was degraded. Even with the conservative assumption of exposure to all degraded PE-PUR foam within the device, the third-party risk assessment concluded that exposure to particulates from degraded foam in first-generation DreamStation devices is unlikely to result in an appreciable harm to health in patients.